1. Field of the Invention
The present invention relates to an image sensor unit, and an image reading apparatus and an image forming apparatus using the image sensor unit. The present invention particularly relates to an image sensor unit enabling light rays from a plurality of light sources to exit from a light guide, and an image reading apparatus and an image forming apparatus using the image sensor unit.
2. Description of the Related Art
Recently, there is a need to enhance the color reproducibility of an umber U-base color being an intermediate color between red R and green G in the result of reading by an image sensor unit used for an image reading apparatus and an image forming apparatus. In such a case, the color reproducibility of the intermediate color can be enhanced by adding a light emitting element emitting a light ray with an emission wavelength corresponding to the intermediate color whose color reproducibility is desired to be enhanced.
Further, there is an original to be read by the image sensor unit which is printed with invisible ink for the purpose of security, and there is a need to also read an ultraviolet wavelength region and a near-infrared wavelength region which are wavelength regions outside the visible region. In such a case, the original printed with the invisible ink can be read by adding light emitting elements emitting light rays with emission wavelengths in the ultraviolet wavelength region and the near-infrared wavelength region as in the above-described method of enhancing the color reproducibility of the intermediate color.
However, when the light emitting elements emitting the light rays with desired emission wavelengths are increased in number, the area of the light entering surface of the light guide needs to be increased for allowing the light rays from all of the light emitting elements to enter through the light entering surface of the light guide. The increase in the area of the light entering surface inevitably leads to an increase in size of the cross-sectional shape of the light guide, bringing about a problem in which the formation of the light guide becomes difficult as well as the light guide and the image sensor unit themselves increase in size.
Thus, a method of providing LEDs at both ends of the light guide so as to increase the total light amount is disclosed in Patent Document 1.    Patent Document 1: Japanese Laid-open Patent Publication No. 9-214675